110 Subsurface Geologic Methods 



in using spore and pollen data for correlating Carboniferous strata, but 

 little work has been done in the United States on these microfossils. An 

 attempt is now being made by the Creole Petroleum Corporation in Vene- 

 zuela to use pollen analysis in correlation problems. 

 According to Wilson/^ 



Spores and pollen meet the requirements for correlation work and have 

 proved their worth, at least in a limited capacity. The chemical nature of 

 spores and pollen is such that most species are resistant to decay. They are 

 varied in their structure and ornamentation, which allows the easy identification 

 of many groups of plants and frequently permits specific determination. They 

 are small and disseminated mainly by air currents. Many species are widely 

 and uniformly spread throughout a region and the sediments in which they 

 may be preserved are numerous. . . . Correlation of strata by fossil spores 

 and pollen has at least three factors of biological background that aid in 

 the accomplishment of results. These are (1) the evolution of floras, (2) the 

 geographic distribution and migration of floras, and (3) the edaphic ecological 

 relations of plants. 



Methods pertaining to collection, maceration of samples, and micro- 

 scopic techniques followed in spore and pollen analysis are clearly treated 

 by Wilson.-" As regards correlation procedures and problems, Wilson 

 presents the following discussion: 



Spores and pollen that occur in the samples may be designated as either 

 dominant or accessory species depending upon their abundance. Usually the 

 dominant species occur in the frequency of five or more percent of the total 

 count in the sample. The accessory species are less frequent and sometimes 

 are not represented by more than a single specimen in a count of one thousand. 

 With the present state of knowledge concerning the distribution of the fossils 

 the dominant species are of most value in correlation studies, but as the vertical 

 and geographical ranges are better understood the accessory species will be- 

 come more significant. This assumption is based upon the possibility that 

 some of the spores or pollen may have come from plants of restricted vertical 

 range in the rocks, of specific paleoecological conditions, or of important index 

 species that produced comparatively few spores or pollen. 



For stratigraphic work the fossils ocurring in the samples may be divided 

 into the following three groups: (1) knowns, (2) unknowns, and (3) those 

 broken beyond recognition. The knowns are those fossils that are recognized 

 as species already described or tentatively given descriptions. They are re- 

 corded and used in correlation work. The unknowns are those fossils that are 

 undescribed and are usually not abundant. Some of these later may be found 

 to be important dominant or accessory species, but in the preliminary work 

 usually are not used. They are lumped under the heading of "unknowns." 

 In the counts it is desirable to have a record of the number of unknown forms 

 and to prepare descriptive illustrations of the more diagnostic types. Those 

 fossils that are broken to the point where they cannot be identified with de- 

 scribed species are ignored in the counts. It is assumed that all species except 

 certain resistant forms will break down in approximately the same ratio or in 

 specific ratios that will not materially affect the final count. 



The number of spores and pollen that should be counted for satisfactory 

 correlation work appears to be based on the use to which the study is directed, 



^'Wilson, L. R., The Correlation of Sedimentary Rocks by Fossil Spores and Pollen: Jour. Sedi- 

 mentary Petrology, vol. 16, no. 3, pp. 110-130, 1946. 

 2» Wilson, L. R., ibid. 



